Detecting devices for detecting particles in the gases or in fluids are required in many situations, such as in manufacturing facilities for foodstuffs, pharmaceuticals, and general industrial products, in laboratories, in indoor environment measurements (testing for allergens), in monitoring atmospheric pollution microparticles, and the like. That which exists in the gas or liquid that is subject to detection by the detecting device includes not only microparticles as simple physical entities (for example, mite carcasses and feces, pollen, sulfides, and the like), but also includes bacteria, funguses (molds), mycoplasmas, and other microorganisms as well.
For example, when detecting atmospheric airborne microparticles or microorganisms, it is possible to collect samples using a filter and then to make observations either directly or after cultivation (for microorganisms), but doing so has drawbacks from the perspective of real-time processing. Given this, an optical particle detecting device has been developed wherein particles are illuminated with an inspection light, and scattered light or florescent light is detected. See, for example, International Patent Application Publication No. WO 2010/080643. An electric signal is outputted when a particle is detected, and thus this is well suited to real-time processing.
In order to increase the inspecting rate for the gas that is subject to analysis (or to increase the analysis efficiency for particles) in the particle detecting device set forth above, one may consider using means for collecting (condensing), into a relatively small volume of the gas flow, particles from a relatively large volume of the gas that is to be inspected. Condensing means can be produced through, for example, establishing a threshold value for a particle sorting device, for sorting particles by a specific particle diameter, between particles and gas molecules. The condensing means (or particle separating means) may be of an impactor method (and inertial impact type), a cyclone method (a centrifugal separating type), or a virtual impactor type, or the like.
For example, in the virtual impactor approach (a virtual inertial impact type), the impact plate in the impactor approach is removed, and instead an opposing nozzle is provided, where the large particles from among the particles that are accelerated by a jet nozzle are captured while passing through the opposing nozzle, to separate the microparticles (described below). An example of this type of condensing method is described in, for example, Yiming Ding et al., Development of a High Volume Slit Nozzle Virtual Impactor to Concentrate Coarse Particles, Aerosol Science and Technology, Mar. 1, 2001.
Moreover, for example, Japanese Unexamined Patent Application Publication No. 2012-141277 describes an example wherein flow rates (flow speeds) in a particle separating device (a cyclone or a virtual impactor) are set in multiple gradations, and a plurality of particle separating device outputs, with different particle selecting characteristics are selected, to specify the particles to be detected (microorganisms, allergens, or the like) depending on the sizes of the applicable particles, whether or not they fluoresce, and the like.
However, in a virtual impactor the particles that are well-suited to selection are determined by the physical specifications of the virtual impactor (the flow path width, the processing flow rate, and the like, of the virtual impactor). When a virtual impactor is used, the inertia that acts on the particles of specific diameters is determined through, for example, setting the gas flow speed (flow rate) of the gas that flows in the virtual impactor to a specific value, to set the separating conditions depending on the size of the particles, to condense the particles or separate the particles.
Because of this, in order to set (adjust) the virtual impactor to a specific vacuum pressure, a vacuum pump, having a specific flow rate specification, and a regulator (a pressure adjusting device) for setting/adjusting the gas flow rate are required separately from the virtual impactor. A regulator is relatively expensive, and produces pressure loss, and, to that extent, prevents the effective use of the vacuum pressure from the pump.
Moreover, even with a structure that is able to select the diameters of particles to be outputted by setting the gas flow rate to a specific value and providing a plurality of virtual impactors having different shapes (referencing, for example, FIG. 33 of Cited Document 2), still the number of virtual impactors is increased, increasing the cost.
Consequently, an aspect of the present invention is to provide a virtual impactor (a particle condensing device) and particle detecting device wherein the processing flow rate of the airflow that includes the particles that are to be condensed can be adjusted without the use of an external device, such as a pressure adjusting device.
Moreover, another aspect of the present invention is to provide a virtual impactor (particle separating device) and particle detecting device structured so as to enable the selection criterion for sorting by particle size to be varied, to eliminate the need for a plurality of particle separating devices.